<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>圆形</title>
</head>
<style>
    div{
        width: 200px;
        height: 200px;
        border: 1px solid black;
        border-radius: 50%;
    }
</style>
<body>
<div>

</div>
</body>
</html>